These planes are manufactured under the US Patent: 746,285 by John W. Carlton – New Britain, CT and George E. Trask – New Britain, CT for the Union Manufacturing Co. – New Britain, CT.
A little different than the Union X Series, which were from patents from John W Carleton and George E Trask as well, but, the x series version had locking nuts.
The 500 series version had just the lever and no locking nuts. The version without locking nuts were only used on some transitionals.
See more Union plane and info here
